/* p5_3.c Toggle LED0 on SAMD21 Xplained Pro at 1 Hz using SysTick
 * This program uses SysTick to generate multiples of millisecond delay.
 * System clock is running at 1 MHz. SysTick is configure
 * to count down from 999 to zero to give a 1 ms delay.
 * A for loop counts how many millisecond the delay should be.
 * When 1000 is used for loop count, the delay is 1000 ms or 1 second.
 * The LED0 is connected to PB30.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

void delayMs(int n);

int main (void)
{
    // make PB30 output for LED
    REG_PORT_DIRSET1 = 0x40000000;     /* make PB30 output for LED */

    while (1) {
        delayMs(1000);      /* delay 1000 ms */
        REG_PORT_OUTTGL1 = 0x40000000;  /* toggle red LED */
    }
}
void delayMs(int n) {
    int i;
    /* Configure SysTick */
    SysTick->LOAD = 1000 - 1;   /* reload with number of clocks per millisecond */
    SysTick->VAL = 0;       /* clear current value register */
    SysTick->CTRL = 0x5;    /* Enable the timer */

    for(i = 0; i < n; i++) {
        while((SysTick->CTRL & 0x10000) == 0) /* wait until the COUNTFLAG is set */
            { }
    }
    SysTick->CTRL = 0;      /* Stop the timer (Enable = 0) */
}